Sequence Stratigraphy and Sea-Level Changes in the Early to Middle Triassic of the Alps: A Global Comparison

Abstract

During Early and early Late Triassic times, the Northern Calcareous Alps (Austria, southern Germany) and the Dolomites (northern Italy) were situated at the margin of the western Tethys. In the Scythian, widespread clastic-carbonate deposition on the shelf prevailed. Carbonate ramps revived in the earliest Anisian. From the late Anisian to the early Ladinian, carbonate ramps evolved to rimmed carbonate platforms. The Dolomites comprise five Scythian sequences, controlled by low amplitude sea-level changes and progressively increasing tectonic subsidence rates. During the Anisian to Ladinian, the sea-level fluctuations increased in amplitude. Five Anisian, three Ladinian and two early Carnian depositional sequences developed. Tectonic subsidence rates changed significantly over intervals of 2–5 Ma in the northwestern Dolomites, but developed steadily in the northeastern Dolomites. The Northern Calcareous Alps comprise two Scythian, five Anisian, four Ladinian and two early Carnian depositional sequences. The completely marine succession were only weakly affected by early tectonics. A distinct increase in subsidence occurred in the late Ladinian, leading to the change from distally steepened ramps to rimmed platforms. Only during this time interval, a rapid tectonic subsidence signal overprinted the sea-level signal.Depositional sequences in the Early to early Late Triassic of the Northern Calcareous Alps and the Dolomites can be correlated, supported by biostratigraphic data. Local controls, for instance varying subsidence rates, were either subdued or can be accounted for by comparing different sections within one study area or both study areas as a whole. Deposition in the northwestern Tethys realm was strongly controlled by basinwide sea-level fluctuations. However, this need not imply eustatic control. In order to assess global sea-level changes, data from the northwestern Tethys have been compared to sea-level data from other Pangean margins. Although biostratigraphic resolution in other basins is limited, depositional sequences of other basins in the northwestern and eastern Tethys, epicontinental seas and the Arctic Sea can be correlated during much of the Scythian to early Carnian: the late Scythian to latest Anisian/earliest Ladinian, the late Ladinian to earliest Carnian and the late early Carnian. Correlative sequences in these basins suggest, that eustatic sea-level changes had a major influence on the development of depositional systems during Scythian to early Carnian times.